Our long-term goals are to understand neuronal mechanisms that underlie hearing in mammals. In the auditory nervous system, all acoustic information from the environment enters the brain by passing from the auditory nerve and synapsing in the cochlear nucleus. In the cochlear nucleus, the relatively homogeneous responses of incoming auditory nerve fibers are transformed into a variety of different response patterns by the different classes of resident neurons, and the resultant signals are in turn transmitted to higher centers. The spectrum of these responses is hypothesized to depend upon the synaptic organization of auditory nerve input, intrinsic neurons, and descending inputs; the types and distribution of receptors, ion channels, and G proteins; and second messengers, all of which form the signaling capabilities in each cell class. In order to understand the how sound is processed at this key auditory nucleus, there is a need to study identified cell populations, to analyze their synaptic connections, and to reveal features of their signal processing capabilities. The present proposal will apply anterograde and retrograde tract tracing methods to identify neurons and their circuits, and immunocytochemical staining procedures to reveal the chemistry of these different neuron populations. In addition, we will apply in vivo and in vitro intracellular recording and staining methods in order to reveal structure-function relationships in the cochlear nucleus at the single cell level. The data from these projects will provide insights into how neurons and their circuits shape the coding process in the central auditory system, and could help in the design of a cochlear nucleus implant for deaf individuals who cannot benefit from a cochlear prothesis.